A computer network includes nodes which communicate data with one another. The nodes may be servers, computers, smartphones, smart appliances, networked vehicles, or other devices which have at least a processor and a network interface. The data may be sent over wired, optical, wireless, or other communication channels, using any of a wide variety of network protocols. The data at a given point in its travel may be plaintext, encrypted, encoded, compressed, divided, or otherwise characterized.
The defined extent of a network may vary according to the definition used. For instance, one may take the view that every node capable of communicating, either directly or indirectly, with a given node X belongs to the same network as node X. In that view, every one of the several billion devices presently connected to the internet belongs to the same network. Alternately, one may use a network definition based on one or more practical realities of network administration. One may decide, for example, that cloud data center servers which are owned by entity A but used by entity B under a service agreement are in a different network than computers which are solely owned and operated by B and in which A has no legal rights. As another example, one could define a first set of nodes as belonging to a different network than a second set of nodes when authentication tokens or certificates that are recognized in the first set of nodes are routinely rejected in the second set, and vice versa. Similarly, networks may be defined in terms of physical connections between nodes, or the relation of nodes to firewalls or to network address translation devices, or nodes' relation to a gateway, or the use or non-use of particular kinds of addresses (e.g., internet protocol addresses versus media access control addresses), or address prefixes, or the use or non-use of bridges or routers, or other technical criteria, or some combination of the foregoing.